Screens or grilles are sometimes used to improve the security of a building. For example, steel bar grilles have been used to deter intruders from entering a premises through a window or door. When used for a window the steel bar grilles are bolted to a wall surface adjacent the window. When used for a doorway the steel bar grilles are pivotally mounted to the doorway and operate as an extra door.
A far more effective intruder resistant screen has been described in our Australian Patent Number 694515. The intruder resistant screen referred to in this patent has been used commercially for many years, with much success.
However, while efficient at keeping out intruders it has since been found that over a period of time these screens are susceptible to corrosion due to penetration by moisture. The moisture seeps through a gap between the mesh screen and the frame.
The problem is that there can be a build up of salts from the moisture. The frame of the intruder resistant screen is made from aluminium, while the woven mesh is made from stainless steel. The electrochemical process that occurs when one type of metal is in contact with another type of metal, in the presence of an electrolyte, will result in corrosion of one or both of the metals.
A strip of plastic tape, such as electrical insulation tape, placed between the mesh and the frame can address the problem. However, the process of fixing the tape is cumbersome and requires precise application at the assembly stage. If the tape is not applied correctly, then parts of the aluminium frame will end up in contact with the stainless steel mesh. Any protection the tape might have given against corrosion will be lost.
This corrosion of the intruder resistant screen weakens the screen, which in turn weakens the security that the screen provides to its user.